steel toughness vs corrosion resistance

Feb 28, 1999
These questions may have been asked a hundred time before, but please humor me. If I understand the term toughness, it would be the opposite of brittleness. Is there a general trend in which, as steel corrosian resistance increases, which appears to be achieved by ramping up the Cr content, that toughness decreases? Looking at Joe T.'s great discussion of the characteristics of various steels, the Carbon steels are the tough guys, far more so than the stainless types. Recent posts suggest that the particle steels may also lack toughness. I'm assuming the brittleness is produced by the presense of Cr. Can someone take a stab at describing what's going on at the molecular level (in the matrix) which makes the stainless steels generally more brittle?


Increasing the carbon content decreases the toughness of the matrix.
Increasing the chromium content decreases the toughness of the matrix.

Put these two together and you wind up with the 400 series stainless steels. As a family they are notoriously brittle (When compared to other families).

Ed, my background is chemistry not metalurgy. Since the matrix is not composed of covalent bonds it does not conveniently fit my model. What you're saying explains a lot. With steel it appears that everything is a series of compromises. To get something you give up something else.

I borrowed an engineering text book on materials. I'll do some more reading.


The *general* rule of thumb I follow is that many alloy elements can increase toughness in small amounts, but most decrease toughness in larger amounts. When I see large amounts -- especially when it comes to carbon and chromium -- I start to worry about toughness at least a little. That's just a general rule, real-world testing sometimes shows this to be wrong.

The CPM steels blow the whole theory, apparently.

CPM throws a curve simply because of the uniformity in the structure. The CPM process for high alloy materials is designed to control carbide content and segregation, two things that will kill toughness.
One of the best books on Tool steel materials is titled "Tool Steels" by Roberts and Carey.
You can get it through ASM International and it gives the best down to earth descriptions on the tool steel families and why they do what they do.